The present invention relates to organic thiol compounds and the preparation thereof. The organic thiol compounds can be utilized to plasticize and/or stabilize halogen-containing polymer compositions, especially poly(vinyl chloride) compositions. The compounds of the present invention are ideally utilized in polymers normally susceptible to deterioration and color change which can occur during processing of the polymer or exposure of the polymer to certain environments and surprisingly also serve as excellent plasticizers.
It is well known that chlorine-containing resins, particularly poly(vinyl chloride) polymers and copolymers, are unstable to heat and light and that the physical properties thereof are degraded upon exposure thereto. This degradation is typically manifested by development of or change in color. It is particularly noticeable in unstabilized polymers, i.e., polymers which do not contain stabilizers. Degradation or discoloration during processing is particularly undesirable in clear or lightly colored plastics. Therefore, it is desirable to prevent or inhibit the discoloration of plastics during processing so as to achieve useful products free of discoloration.
In order to minimize the discoloration and deterioration of various halogen-containing polymers such as vinyl chloride polymers and copolymers, various stabilizers such as lead-, cadmium-, and tin-based stabilizers have been developed and utilized. However, in recent years environmental pollution caused by the toxicity of the heavy metal residues and ecological considerations have stimulated further evaluation of such compounds and generated a search for alternative approaches.
Various compounds have been proposed for use in stabilizing halogen-containing polymers:
U.S. Pat. No. 3,928,285 to Gough et al. relates to a synergistic stabilizer composition comprising an organotin borate and an organic thiol.
U.S. Pat. No. 4,948,827 to Christidis relates to a thiophenol, prepared by reduction of tertiary butyl-4-toluenesulfonyl-2-chloride with the zinc-sulfuric acid couple, which reportedly can be used as a stabilizer for vinyl chloride polymers, as a chain-transfer agent, and as a peptizer.
European Patent Application No. EP 0 890 608 A2 relates to both flexible and rigid vinyl chloride polymer compositions incorporating a latent mercaptan-containing heat stabilizer which are reportedly substantially free from the offensive odor typically associated with mercaptans and are protected during processing by the degradation products of the latent (i.e., blocked) mercaptan, which include a free mercaptan. The free mercaptan thus released reportedly enhances the activity of metallic-based heat stabilizers such as zinc carboxylates and organotin carboxylates and mercaptides in the polymer composition. Other products of the degradation are believed to include carbocations of the blocking moiety which are stabilized by a molecular structure in which the electron deficiency is shared by several groups. The latent mercaptan comprises a 2-S-(tetrahydropyranyl)thioalkanol or a carboxylic acid ester thereof.
European Patent Application No. EP 0 945 484 A1 relates to compositions comprising halogen-containing polymers such as PVC resins which are reportedly stabilized against heat by a synergistic combination of a free mercaptan and a metal-based stabilizer and/or a Lewis acid such as zinc chloride.
Organic thiol compounds and routes for their preparation are disclosed herein. The organic thiol compounds of the present invention, when blended with a halogen-containing polymer such as poly(vinyl chloride) or derivatives thereof, provide numerous functions which include serving as plasticizers, stabilizers, and dehydrochlorination retarders. The organic thiol compounds of the present invention have a substantially reduced or even lack a characteristic odor typically associated with thiol compounds.
The organic thiols of the present invention are aromatic compounds having at least one sulfhydryl group attached either directly or indirectly to an aromatic ring. The aromatic compound may contain one or more aromatic rings and at least one sulfhydryl substituent, as well as other groups such as an ester group, and the like. The organic thiols can generally be described by the formula: 
wherein R1 and R2, independently, comprise straight chain or branched alkyls having from 1 or 2 to about 15 carbon atoms, and preferably from about 4 to about 15 carbon atoms, or an aromatic or a substituted aromatic having from about 6 to about 15 carbon atoms and wherein, independently, n is either 0, 1, 2, or 3, m is either 0, 1, 2, or 3, and p is either 0, 1, 2, or 3, with the proviso that m+n+p=6 or less. It is to be understood that when, independently, m, n, and/or p are greater than 1, the individual repeat groups are each attached to a different carbon atom on the benzene ring.
Independent exemplifications of R1 and R2 are 2-ethylhexyl, isooctyl, isodecyl, benzyl and butyl.
Examples of compounds which can be formed from the above formula include: 
The various compounds of the above-disclosed general formula wherein m=0 can be synthesized substantially as follows. In a first step, a desired amount of an hydroxy aromatic acid is placed in a reaction vessel together with a large molar excess of an alcohol having from 1 to about 3 carbon atoms, preferably methanol or ethanol. From about 0.05 to about 0.5 mole, per mole of the starting acid, of a very strong acid, i.e., one having a concentrated pH of at least 1 to about 3, such as H2SO4, para-toluenesulfonic acid, or hydrochloric acid, is added to the mixture, and the mixture is then heated either under air or preferably under inert conditions, such as under nitrogen, generally to the reflux temperature of the alcohol, for a sufficient length of time until the reaction is complete, a condition which can be established through periodic analysis.
The hot solution is then poured into a quantity of ice water. Then, the precipitate is filtered off and washed on the filter until the pH of the wash liquid is neutral. The filtered product is then dried to give an hydroxy aromatic ester, which can be purified further by conventional methods, if desired.
A desired amount of the above-noted ester is added to a reaction vessel along with an N,N-dialkylthiocarbamoyl halide such as N,N-dimethylthiocarbamoyl chloride (about 1-3 moles per mole of ester), a base such as DABCO (about 1-3 moles per mole of ester), and N,N-dimethylformamide (about 1-3 liters per mole of ester). The mixture is stirred at room temperature (e.g., 15xc2x0 C. to about 30xc2x0 C.) for a suitable reaction time, and a suitable quantity of water is then added to induce precipitation of a solid which is filtered off and washed on the filter until the pH of the wash liquid is neutral. The resulting second step intermediate product (the corresponding O-substituted N,N-dimethylthiocarbamate) is subsequently dried.
The second step intermediate product is transferred to a suitable reaction vessel and heated preferably in an oil bath or the like to a temperature from about 180xc2x0 C. to about 250xc2x0 C. and desirably from about 220xc2x0 C. to about 235xc2x0 C. until the reaction is complete, generally in about 20 minutes to about 2 hours. Then, after cooling to about 60xc2x0 C. to about 90xc2x0 C., the reaction vessel is purged with nitrogen or other chemically unreactive gas, and an aqueous solution of a base such as NaOH or KOH is subsequently added in an amount that is at least sufficient to cause hydrolysis of the thiocarbamate and ester groups. The mixture is heated under reflux to induce complete reaction and then cooled to room temperature and acidified to a pH generally less than 4 in any manner such as with a 10 percent aqueous solution utilizing an acid as stated above. The recovered mercapto acid product from the third step is washed with suitable quantities of water and dried, preferably under a vacuum.
In the final step of the synthesis, the intermediate product from the third step is added to a reaction vessel equipped with a suitable stirring apparatus, a water separator, and a reflux condenser, along with an alkyl alcohol having from 1 to 15 carbon atoms in an amount from about 1 to about 2 molar equivalents per carboxyl group in the mercapto acid, benzene or other suitable entraining agent for water (about 0.5 to 2 L per mole of mercapto acid), and a strong acid (about 0.1 to 0.3 mole per mole of mercapto acid) as defined above. The mixture is heated to the reflux temperature for a sufficient time to induce extensive reaction, typically approximately three hours, or until all the solid is dissolved. The solution is cooled to room temperature and poured into ice water, and the organic layer is washed in succession with a NaHCO3 or Na2CO3 solution and water. The organic layer is dried over a drying agent such as anhydrous MgSO4. The dried solution is decolorized with activated carbon, filtered, and distilled to remove the benzene and other volatile impurities. The final product is generally an oil or low melting solid having a structure defined by the general formula of the present invention.
When m in the general formula is unequal to 0, the HSR2OOC groups of the thiols of this invention can be introduced by the direct esterification of COOH groups with thioalkanols (HSR2OH), using methods that are well-known to those skilled in the art. For example, compound 11 in which R2 is xe2x80x94(CH2)6xe2x80x94 has been prepared by the esterification of isophthalic acid with two molar equivalents of 6-mercapto-1-hexanol in the presence of a catalytic amount of concentrated H2SO4.
Bis(2-ethylhexyl) 5-mercaptoisophthalate is one such compound which is disclosed by the general formula of the present invention when n is 1, m is 0, p is 2, and R1 is 2-ethylhexyl, and is also shown as specific formula 4. The synthetic route disclosed hereinbelow for preparation of the bis(2-ethylhexyl) 5-mercaptoisophthalate compound is based in part on a Newman-Kwart reaction, as in the general route described above.
Bis(2-ethylhexyl) 5-mercaptoisophthalate Can be Synthesized as Follows:
To a 1-L round-bottom flask equipped with a magnetic stirring bar were added 187.8 g (1 mol) of 5-hydroxyisophthalic acid commercially available from Aldrich (purity approximately 97%) and 500 mL (12.3 mol) of methanol. After the addition of 28 mL of concentrated H2SO4, the mixture was heated to the reflux temperature and stirred under reflux for 4 hours. The hot solution was poured into 500 mL of ice water. Then, the white solid product was filtered off and washed on the filter with several portions of water until the pH of the wash liquid was neutral. The product was dried under vacuum, preferably at 60xc2x0 C. overnight, to give 206.8 g of dimethyl 5-hydroxyisophthalate. Testing on the composition revealed the following data: mp 164-166xc2x0 C.; GC purity greater than 99%; yield 98.2%; 1H NMR (in CDCl3+DMSO-d6w/TMS, ppm): 3.68 (s, 6H, OCH3), 7.45 (s, 2H, CH), 7.89 (s, 1H, CH), 9.35 (broad, 1H, OH); {1H}13C NMR (in CDCl3+DMSO-d6w/TMS, ppm): 51.92 (OCH3), 120.50 (C4, C6), 121.10 (C2), 131.15 (C1, C3), 157.36 (C5), 165.85 (COOR); 1H-13C NMR (in CDCl3+DMSO-d6 w/TMS, ppm): 51.92 (quartet, OCH3, 1JCH=147 Hz), 120.50 (d, C4, C6, 1JCH=164.4 Hz), 121.10 (d, C2, 1JCH=168.3 Hz), 131.15 (s, C1, C3), 157.36 (s, C5), 165.85 (s, COOR); GC-MS (in acetone): 210 (M+).
To a 150-mL round-bottom flask equipped with a magnetic stirring bar were added dimethyl 5-hydroxyisophthalate, N,N-dimethylthiocarbamoyl chloride, DABCO (1,4-diazabicyclo[2.2.2]octane), and 50 mL of N,N-dimethylformamide. The mixture was stirred at room temperature for 5 hours, and 100 mL of water then was added slowly. The orange solid gradually disappeared, and the solution became light brown. An additional 100 mL of water was added to induce the precipitation of a white solid, which was filtered off and washed on the filter with portions of water until the pH of the wash liquid was neutral. The product was dried, preferably under vacuum at 60xc2x0 C. overnight, to give 1-O-3,5-bis(methoxycarbonyl)phenylene N,N-dimethylthiocarbamate as a white powder. Testing of the compound revealed the following: mp 114.5-116.5xc2x0 C.; 1H NMR (in CDCl3w/TMS, ppm): 3.38 (s, 3H, NCH3), 3.46 (s, 3H, NCH3), 3.94 (s, 6H, OCH3), 7.93 (s, 2H, CH), 8.58 (s, 1H, CH); {1H}13C NMR (in CDCl3w/TMS, ppm): 38.85 (NCH3), 43.39 (NCH3), 52.51 (OCH3), 127.96 (C4), 128.36 (C2, C6), 131.54 (C3, C5), 153.86 (C1), 165.30 (COOR), 186.84 (OC(S)NR2).
As shown by the following table, reaction yield for 1-O-3,5-bis(methoxycarbonyl)phenylene N,N-dimethylthiocarbamate varied as a function of the molar ratio of the reactants.
In a test tube containing a magnetic stirring bar, 0.1 g (0.336 mmol) of 1-O-3,5-bis(methoxycarbonyl)phenylene N,N-dimethylthiocarbamate was heated in an oil bath at a constant temperature, preferably about 230-235xc2x0 C., for a selected time, preferably at least 20 minutes. As can be seen from the following table, reaction yield varied as a function of time and temperature.
The white solid first melted into a yellowish oil, then gradually became dark brown. After cooling to room temperature, a tar-like solid was obtained. Recrystallization from methanol gave 1-S-3,5-bis(methoxycarbonyl)phenylene N,N-dimethylthiocarbamate as a gray solid having the following characteristics: mp 117-118xc2x0 C.; 1H NMR (in CDCl3w/TMS, ppm): 3.06 (s, 3H, NCH3), 3.12 (s, 3H, NCH3), 3.94 (s, 6H, OCH3), 8.34 (s, 2H, CH), 8.69 (s, 1H, CH); {1H}13C NMR (in CDCl3 w/TMS, ppm): 37.06 (N(CH3)2), 52.53 (OCH3), 130.90 (C4), 131.44 (C3, C5),131.58 (C2, C6),140.87 (C1), 165.81 (COOR), 165.94 (SC(O)NR2); 1H-13C NMR (in CDCl3 w/TMS, ppm): 37.06 (quartet, N(CH3)2, 1JCH=139.6 Hz), 52.53 (quartet, OCH3, 1JCH=147.34 Hz), 130.90 (doublet of triplets, C4, 1JCH=167.65 Hz, 3JCH=6.448 Hz), 131.44 (C3, C5),131.58 (doublet of doublets, C2, C6, 1JCH=168.3 Hz, 3JCH=6.448 Hz),140.87 (C1), 165.81 (COOR), 165.94 (SC(O)NR2).
The 1-O-3,5-bis(methoxycarbonyl)phenylene N,N-dimethylthiocarbamate (112.2 g, 0.377 mol) was placed in a 2-L two-necked round-bottom flask equipped with a magnetic stirring bar, a condenser, and a thermometer. The flask was submerged in an oil bath preheated to 232-234xc2x0 C. and kept at that temperature for 2 hours. The resulting dark brown oil was allowed to cool to about 80xc2x0 C. Then the thermometer was replaced by a gas inlet tube, and the system was purged with nitrogen before 850 mL of 2.7 N NaOH was added. The mixture was heated under reflux for 2 hours, cooled to room temperature, and acidified to pH less than 4 with 10% aqueous HCl. Then the beige solid product was washed, preferably 3 times, with 400-mL portions of water and dried under vacuum at 60-70xc2x0 C. to obtain 5-mercaptoisophthalic acid. Testing of the compound revealed the following properties: yield 67.5 g (90.3%); mp 240-246xc2x0 C.; 1H NMR (in DMSO-d6w/TMS, ppm): 3.02 (s, 1H, SH), 8.24 (s, 2H, CH), 8.37 (s, 1H, CH), 13.50 (broad, 2H, COOH); {1H}13C NMR (in DMSO-d6 w/TMS, ppm): 129.43 (C2),130.88 (C4, C6),134.74 (C1, C3),136.51 (C5), 166.91 (COOH); 1H-13C NMR (in DMSO-d6w/TMS, ppm): 129.43 (d, C2, 1JCH=167.39 Hz), 130.88 (d, C4, C6, 1JCH=165.27 Hz), 134.74 (C1, C3),136.51 (C5),166.91 (COOH).
In the final step of the synthesis, to a 1-L round-bottom flask equipped with a magnetic stirring bar, a water separator, and a condenser were added 65.1 g (0.328 mol) of powdered 5-mercaptoisophthalic acid, 113 mL (94.2 g, 0.723 mol) of 2-ethyl-1-hexanol, 200 mL of benzene, and 4 mL of concentrated H2SO4. After the mixture had been heated under reflux for a sufficient time, approximately 3 h, about 12 mL (0.67 mol) of water had been collected by the water separator. The mixture was allowed to reflux until all of the solid was dissolved, generally about 24 hours, and a dark brown solution was obtained. After cooling to room temperature, the solution was poured into ice water, and the organic layer was washed in succession with 50 mL of saturated NaHCO3 solution and two 50-mL portions of water. The organic layer was dried over anhydrous MgSO4, and the dried solution was decolorized with ca. 10 g of activated carbon. After filtration, most of the benzene was removed by distillation at atmospheric pressure, and the excess 2-ethyl-1-hexanol and a trace amount of benzene were then removed by distillation at about 1 torr. The residual oil was bis(2-ethylhexyl) 5-mercaptoisophthalate. Testing on the compound revealed the following data: yield 132.7 g (95.5%); GC purity greater than 89%; 1H NMR (in CDCl3w/TMS, ppm): 0.94 (m, 8H, CH2), 1.40 (m, 20H, CH2CH3), 1.75 (m, 2H, CH), 3.77 (s, 1H, SH), 4.28 (d, 4H, CH2),8.11 (s, 2H, CH), 8.43 (s, 1H, CH); {1H}13C NMR (in CDCl3 w/TMS, ppm): 11.125 (C6xe2x80x2/C8xe2x80x2), 14.031 (C6xe2x80x2/C8xe2x80x2), 23.050 (C5xe2x80x2/C7xe2x80x2), 24.211 (C5xe2x80x2/C7xe2x80x2), 29.154 (C3xe2x80x2/C4xe2x80x2), 30.760 (C3xe2x80x2/C4xe2x80x2), 39.196 (C2xe2x80x2), 68.107 (C1xe2x80x2), 127.87 (C2), 132.23(C1,C3),133.09 (C5),134.14 (C4, C6),165.47 (COOR); GC-MS (in acetone): 422 (M+).
The reaction sequence for the synthesis just described is as follows: 
The organic thiol compounds disclosed by the present invention can be used as additives for polymeric compounds, wherein, for example, the organic thiols can serve as plasticizers as well as stabilizers. The organic thiols are free of metal, and are not used in conjunction with any other metal-based stabilizers or Lewis acids. By metal-based stabilizers it is meant any metal compound, salt, complex, or the like of any of the metals as set forth in groups 1-8 of the periodic table such as, but not limited to the heavy metals, for example cadmium, mercury, lead, and the like as well as other generally environmentally unfriendly or undesirable compounds. Examples of specific metal-based stabilizers which are avoided include those set forth in European Patent Application EP 0 945 484 A1 at least on page 3 thereof. The substantially free amount of the various metal-based stabilizers is generally less than about 2 percent, desirably less than about 1 percent, and preferably less than about 0.5 percent by weight based upon 100 total parts by weight of the one or more halogen-containing polymers or copolymers. The polymer compositions of the present invention are also generally substantially free of various Lewis acids such as boron trifluoride, aluminum chloride, zinc chloride, methyltin trichloride, dibutyltin dichloride, and the like. Such acids when contained in the polymeric composition are generally less than about 0.5 percent, desirably less than about 0.1 percent, and preferably less than about 0.01 percent by weight per 100 total parts by weight of all halogen-containing polymers or copolymers.
The polymers utilized in the present invention include any organic chlorine- or bromine-containing polymers or resins in which the halogen is attached directly to a carbon atom. Polymers and/or monomers thereof useful to the present invention include, but are not limited to, poly(vinyl chloride) (PVC), poly(vinylidene chloride), poly(vinyl bromide), poly(vinylidene bromide), chlorinated poly(vinyl chloride), chlorinated polyethylene, chlorinated natural or synthetic rubber, polychloroprene, rubber hydrochloride, or chlorinated polystyrene, and combinations and copolymers thereof. The molecular weight of such polymers can vary over a wide range, and they can have a number average molecular weight of from about 5,000 to about 1,000,000.
Such polymers can also contain other plasticizers in addition to the compounds of the present invention, and where appropriate, such polymers can be plastisols, organisols, and the like.
The above noted chlorine- or bromine-containing polymers are made from monomers forming the same such as vinyl chloride, vinylidene chloride, and the like, or are a copolymer made from a mixture of monomers comprising, desirably, at least about 70% by weight of vinyl chloride, based on the total monomer weight. Examples of the copolymers include those made from vinyl chloride and from about 1 to about 30% of a copolymerizable ethylenically unsaturated monomer such as vinyl acetate, vinyl butyrate, vinyl benzoate, vinylidene chloride, diethyl fumarate, diethyl maleate, other alkyl fumarates and maleates, vinyl propionate, methyl acrylate, 2-ethylhexyl acrylate, butyl acrylate and other alkyl acrylates, methyl methacrylate, ethyl methacrylate, butyl methacrylate and other alkyl methacrylates, methyl alpha-chloroacrylate, styrene, trichloroethylene, vinyl ethers such as vinyl ethyl ether, vinyl chloroethyl ether and vinyl phenyl ether, vinyl ketones such as vinyl methyl ketone and vinyl phenyl ketone, 1-fluoro-2-chloroethylene, acrylonitrile, chloroacrylonitrile, allylidene diacetate and chloroallylidene diacetate. Typical copolymers include vinyl chloride-vinyl acetate (e.g. 96:4 sold commercially as VYNW), vinyl chloride-vinyl acetate (e.g. 87:13), vinyl chloride-vinyl acetate-maleic anhydride (e.g. 86:13:1), vinyl chloride-vinylidene chloride (e.g. 95:5), vinyl chloride-diethyl fumarate (e.g. 95:5), and vinyl chloride-2-ethylhexyl acrylate (e.g. 80:20).
Preferred polymers include poly(vinyl chloride) and poly(vinyl bromide). Preferred copolymers include vinyl chloride-vinyl acetate, vinyl chloride-vinylidene chloride, and other vinyl chloride copolymers.
The organic thiol compounds according to the present invention can be added to or blended with the above described polymers in any suitable amount, generally from about 1 to about 100 parts by weight per 100 total parts by weight of all of the one or more polymers or copolymers, depending on the desired properties of the final product. As stated above, the organic thiol compounds of the present invention are particularly suitable for serving as both stabilizers and plasticizers. A semi-rigid composition of the present invention would desirably contain from about 1 to about 25 parts of the organic thiol compound per 100 parts by weight of a polymer defined above. A flexible composition of this invention contains from about 25 to about 100 parts of the organic thiol compound per 100 parts of polymer utilized in the present invention. The organic thiol compounds can be incorporated into the resin by any one of many known methods that provide for uniform distribution of additives throughout resin compositions, such as, for example, mixing in an appropriate mill, mixer, or Banbury apparatus.
Depending on the end use, further additives, known to the art and to the literature or to those of ordinary skill in the art, can be added in conventional amounts to the above noted polymers, such as certain other stabilizers and costabilizers, lubricants, plasticizers, extenders, impact modifiers, fillers, pigments, antioxidants, dyes, ultraviolet light absorbing agents, densifying agents, and the like.
As stated above, the organic thiols greatly enhance the heat stability of halogenated resins, which are known to undergo rapid thermal degradation under the conditions found in the processes to which these resins are subjected, such as, for example, calendering, extrusion, injection molding, and end usage at elevated temperatures. For example, poly(vinyl chloride) is known to undergo a rapid and sequential elimination of hydrogen chloride, or dehydrochlorination, at elevated process temperatures. Other halogenated resins are known to undergo similar dehydrohalogenation reactions. Dehydrochlorination in PVC can initiate at labile chlorines that are associated with irregularities in the molecular chain, such as branches or double bonds. Once free, the HCl promotes further degradation of the poly(vinyl chloride) through unzipping of additional hydrogen chloride from the polymer chain. The primary functions of heat stabilizers in PVC are to depress hydrogen chloride elimination and discoloration. In addition to functioning as heat stabilizers, the organic thiols of the present invention are often effective plasticizers and frequently serve or function as both a heat stabilizer and a plasticizer. Thus, in many polymer compositions such as PVC, organic thiols of the present invention serve as heavy-metal-free or metal-based-free stabilizers and plasticizers, a unique combination.
The organic thiols of the invention thus unexpectedly improve the processing properties of the polymers, further providing cost and efficiency improvements to resin processors. The disclosed thiols also reduce odor problems associated with the processing of resins stabilized thereby and provide increased resistance to resin yellowing associated with thermal degradation.
The following examples serve to illustrate, but not to limit, the present invention.